The invention relates generally to fiber optic chemical sensors (FOCS) and more particularly to water repellent FOGS.
A fiber optic is an optical waveguide which transmits light by total internal reflection at the core/clad interface, which occurs when the refractive index of the clad is less than the index of the core. Optical fibers have been used in a wide variety of sensors, known as "optrodes" or "fiber optic chemical sensors" (FOCS), which can detect various chemical species or physical parameters.
U.S. patent application Ser. No. 150,197, filed Jan. 29, 1988, now U.S. Pat. No. 4,929,049, issued May 29, 1990, describes a refractive index FOCS in which a thin film metal clad is formed on the core of sufficient thickness so that analyte molecules adsorbed on the metal clad produce a localized change in refractive index which modulates light transmission through the core. A problem exists when using the refractive index FOCS in an aqueous medium because of the high affinity of the water molecules for the metal clad, which interferes with the measurement. In other words, the FOCS responds to both vapor and liquid water in a manner similar to a non-aqueous analyte.
Accordingly, it would be desirable to make a FOCS, particularly a refractive index FOCS, substantially water repellent while maintaining its sensing characteristics.
The science of making surfaces water repellent is very old. In the modern scientific approach, hydrophobic materials such as silicon-based organometallic polymers, polytetrafluorethylene (Teflon--a registered trademark of DuPont), and the like are applied to the surface by using a variety of techniques to make surfaces water repellent. However, these techniques are generally not applicable to FOCS as it is necessary to impart water repellency while allowing analyte molecules to reach the sensing surface.